# A-level Edexcel Maths - Proofs

Does anyone know what the exact proofs we need to learn are? For example, the sum of an arithmetic series.

I know that sin^2(x) + cos^2(x) = 1 also has to be learned but I'm not sure what else there is. I tried checking the syllabus but I'm still confused. Learning them would basically guarantee those few marks too
Those are formulas, not proofs.

This is good:
Original post by JeffDaPenguin
Those are formulas, not proofs.
This is good:

Oh yes what I meant was, questions that ask to prove the formulas. I.e, prove that the sum of an arithmetic series is n/2(2a+(n-1)dI hope that makes sense? Thanks for the yt link
Original post by poppjngcandy
Oh yes what I meant was, questions that ask to prove the formulas. I.e, prove that the sum of an arithmetic series is n/2(2a+(n-1)dI hope that makes sense? Thanks for the yt link

It's not hard to search for 'proof' in the specification.
I'd say the only two "you must know this" results are the sums of arithmetic/geometric progressions. It also says "Understand and use double angle formulae; use of formulae for sin (A ± B),cos (A ± B), and tan (A ± B), understand geometrical proofs of these formulae." but I'd hesitate to say that means you'd be expected to be able to prove them.
Original post by poppjngcandy
Does anyone know what the exact proofs we need to learn are? For example, the sum of an arithmetic series.
I know that sin^2(x) + cos^2(x) = 1 also has to be learned but I'm not sure what else there is. I tried checking the syllabus but I'm still confused. Learning them would basically guarantee those few marks too

A couple of "show that" questions I think I can recall seeing are:

1) Starting with the standard expressions for sin(A + B) and cos(A + B) (both given), derive the standard expression for tan(A + B).

2) Starting with expressions y(t) and x(t) for the vertical and horizontal displacement of a projectile, eliminate t so as to end up with an expression for y as a function of x.